Hot-melt glue guns are becoming increasingly popular for various adhesive applications. An example of a glue gun adapted to be held in the hand of an operator and used to dispense hot-melt adhesives can be found in U.K. Patent Specification No. 1402648.
In general, it is well known to provide glue guns adapted to be held in the hand of an operator with a melt chamber in which an end portion of a stick is received and melted by heat supplied to the melt chamber. Progressive melting of the glue stick may be achieved by pressing the glue stick into the melt chamber by means of the operator's thumb or a mechanical feed mechanism. Melted adhesive is dispensed from a nozzle of the gun as the stick is fed into the melt chamber and melted therein.
Certain polyester-based adhesives are known in the art to be useful in glue gun applications; however, these adhesives suffer several disadvantages (see U.S. Pat. No. 4,618,643).
Polyester adhesives are normally used in powder, film, or web form for bonding and laminating applications. They can be processed easily in extruders where temperatures can be raised to obtain the lower melt viscosities needed for the application. However, with hand-held glue guns, it is not practical or safe to use processing temperatures greater than 190.degree. C. or adhesives with melt viscosity values greater than about 50,000 centipoise (cP) at 190.degree. C. for preparing bonds. Most polyester adhesives have melt viscosity values in the range of about 75,000 to about 300,000 cP at 190.degree. C. and are not suitable for these applications. In general, if the inherent viscosity (I.V.) of polyesters is reduced to levels so that the melt viscosity at application temperature is less than about 50,000 cP, the bonding properties of the polyester adhesive for hot-melt applications are often reduced to an unacceptable level due to faster crystallization times and shorter open time of the adhesive and the reduced tensile strength of the bulk polymer.
It would be desirable to have a polyester formulation that has excellent bonding properties and acceptable melt viscosities for glue gun adhesive applications.